Cochlear electrode array

ABSTRACT

A cochlear lead includes a plurality of electrode assemblies partially embedded in a flexible body configured to stimulate an auditory nerve from within a cochlea. Each of the electrode assemblies includes a flexible electrically conductive material forming a plurality of support structures and an electrode pad attached a support structure, the electrode pad having a surface that is configured to be exposed to cochlear tissue and fluids and has a charge transfer to the cochlear tissue and fluids that is higher than the flexible electrically conductive material.

RELATED DOCUMENTS

The present application claims the priority of U.S. patent applicationSer. No. 13/516,982 (now issued as 9056196) and claims priority under 35U.S.C. 119(a)-(d) or (f) and under C.F.R. 1.55(a) of previousInternational Patent Application No.: PCT/US2010/060306, filed Dec. 14,2010, entitled “Cochlear Electrode Array” which claims the benefit under35 U.S.C. §119(e) of U.S. Provisional Application No. 61/288,201,entitled “Cochlear Electrode Array” filed Dec. 18, 2009, whichapplications are incorporated herein by reference in their entirety.

BACKGROUND

In human hearing, hair cells in the cochlea respond to sound waves andproduce corresponding auditory nerve impulses. These nerve impulses arethen conducted to the brain and perceived as sound.

Damage to the hair cells results in loss of hearing because sound energywhich is received by the cochlea is not transduced into auditory nerveimpulses. This type of hearing loss is called sensorineural deafness. Toovercome sensorineural deafness, cochlear implant systems, or cochlearprostheses, have been developed. These cochlear implant systems bypassthe defective or missing hair cells located in the cochlea by presentingelectrical stimulation directly to the ganglion cells in the cochlea.This electrical stimulation is supplied by an electrode array which isimplanted in the cochlea. The ganglion cells then generate nerveimpulses which are transmitted through the auditory nerve to the brain.This leads to the perception of sound in the brain and provides at leastpartial restoration of hearing function.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various embodiments of theprinciples described herein and are a part of the specification. Theillustrated embodiments are merely examples and do not limit the scopeof the claims.

FIG. 1 is a diagram showing an illustrative cochlear implant system inuse, according to one embodiment of principles described herein.

FIG. 2 is a diagram showing external components of an illustrativecochlear implant system, according to one embodiment of principlesdescribed herein.

FIG. 3 is a diagram showing the internal components of an illustrativecochlear implant system, according to one embodiment of principlesdescribed herein.

FIG. 4 is a perspective view of an illustrative electrode array beinginserted into a cochlea, according to one embodiment of principlesdescribed herein.

FIG. 5 is a top view of a patterned sheet of electrochemically activatedmaterial attached to a sacrificial substrate, according to oneembodiment of principles described herein.

FIG. 6 is a top view of a patterned sheet of flexible conductivematerial which is attached to underlying electrode pads, according toone embodiment of principles described herein.

FIGS. 7A and 7B are a perspective and cross-sectional view,respectively, of one illustrative embodiment of a composite electrodeassembly having an integral wire carrier, according to one embodiment ofprinciples described herein.

FIGS. 8A and 8B are a perspective and cross-sectional view,respectively, of one illustrative embodiment of a composite electrodeassembly having an integral wire carrier, according to one embodiment ofprinciples described herein.

FIG. 9 is a cross-sectional view of an illustrative cochlear lead havingan electrode pad exposed at an outer surface of a flexible body of thecochlear lead, according to one embodiment of principles describedherein.

FIG. 10 is a flowchart diagram of an illustrative method for forming anelectrode array, according to one embodiment of principles describedherein.

FIG. 11 is a top view of a patterned sheet of flexible conductivematerial which is attached to a sacrificial substrate, according to oneembodiment of principles described herein.

FIG. 12 is a top view of a patterned sheet of electrochemicallyactivated material attached over apertures in a flexible conductivematerial, according to one embodiment of principles described herein.

FIG. 13 is a cross sectional view of an electrode assembly which isencapsulated in a flexible body, according to one embodiment ofprinciples described herein.

FIG. 14 is a cross sectional view of an electrode assembly whichincludes a surface layer on an electrode pad, according to oneembodiment of principles described herein.

FIG. 15 is a flowchart showing one illustrative method for forming anelectrode in a cochlear electrode array, according to one embodiment ofprinciples described herein.

Throughout the drawings, identical reference numbers designate similar,but not necessarily identical, elements.

DETAILED DESCRIPTION

As mentioned above, individuals with hearing loss can be assisted by anumber of hearing devices, including cochlear implants. Cochlearimplants are made up of both external and implanted components. Theexternal components detect environmental sounds and convert the soundsinto acoustic signals. These acoustic signals are separated into anumber of parallel channels of information, each representing a narrowband of frequencies within the perceived audio spectrum. Ideally, eachchannel of information should be conveyed selectively to a subset ofauditory nerve cells that normally transmit information about thatfrequency band to the brain. Those nerve cells are arranged in anorderly tonotopic sequence, from the highest frequencies at the basalend of the cochlear spiral to progressively lower frequencies towardsthe apex. An electrode array is inserted into the cochlea and has anumber of electrodes which corresponded to the tonotopic organization ofthe cochlea. Electrical signals are transmitted through a wire to eachof the electrodes in the electrical array. When an electrode isenergized, it transfers the electrical charge to the surrounding fluidsand tissues. This triggers the ganglion cells to generate nerve impulseswhich are conveyed through the auditory nerve to the brain and perceivedas sound.

In the following description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present systems and methods. It will be apparent,however, to one skilled in the art that the present systems and methodsmay be practiced without these specific details. Reference in thespecification to “an embodiment,” “an example,” or similar languagemeans that a particular feature, structure, or characteristic describedin connection with the embodiment or example is included in at leastthat one embodiment, but not necessarily in other embodiments. Thevarious instances of the phrase “in one embodiment” or similar phrasesin various places in the specification are not necessarily all referringto the same embodiment.

A cochlear electrode array is a thin, elongated, flexible carriercontaining several longitudinally disposed and separately connectedstimulating electrode contacts, conventionally numbering about 6 to 30.According to one illustrative embodiment, the electrode array may beconstructed out of biocompatible silicone, platinum-iridium wires, andplatinum electrodes. This gives the distal portion of the lead theflexibility to curve around the helical interior of the cochlea.

To place the electrode array into the cochlea, the electrode array maybe inserted through a cochleostomy or via a surgical opening made in theround window of the cochlea. The electrode array is inserted through theopening into the scala tympani, one of the three parallel ducts thatmake up the spiral-shaped cochlea. The electrode array is typicallyinserted into the scala tympani duct in the cochlea to a depth of about13 to 30 mm.

In use, the cochlear electrode array delivers electrical current intothe fluids and tissues immediately surrounding the individual electrodecontacts to create transient potential gradients that, if sufficientlystrong, cause the nearby auditory nerve fibers to generate actionpotentials. The auditory nerve fibers branch from cell bodies located inthe spiral ganglion, which lies in the modiolus, adjacent to the insidewall of the scala tympani. The density of electrical current flowingthrough volume conductors such as tissues and fluids tends to be highestnear the electrode contact that is the source of such current.Consequently, stimulation at one contact site tends to selectivelyactivate those spiral ganglion cells and their auditory nerve fibersthat are closest to that contact site.

Improved charge transfer from the surface of the electrode to thesurrounding fluid and tissues reduces impedances and improves batterylife of the cochlear implant system. While smooth platinum is a reliablestimulating surface for cochlear implants, it has been discovered thatthere are other biocompatible materials and surface structures that havebetter charge transfer between the electrode and surrounding tissues.One of these materials is activated iridium. To activate iridium, theiridium surface undergoes a number of electrochemical cycles in awater-based electrolyte to develop an “activated” iridium oxide surfacethat is superior to platinum for charge transfer.

However, iridium is a relatively brittle material compared to platinum.As a consequence, iridium may be less suitable for other electrodemanufacturing steps which are used to form some types of cochlearelectrode arrays. The new techniques and structures described belowmaximize the charge transfer of the electrode surface while maintainingthe manufacturability of the electrode arrays. These automated orsemi-automated techniques also minimize part-to-part variability anddefects which result from less controlled manual processes.

FIG. 1 is a diagram showing one illustrative embodiment of a cochlearimplant system (100) having a cochlear implant (300) with an electrodearray (195) that is surgically placed within the patient's auditorysystem. Ordinarily, sound enters the external ear, or pinna, (110) andis directed into the auditory canal (120) where the sound wave vibratesthe tympanic membrane (130). The motion of the tympanic membrane isamplified and transmitted through the ossicular chain (140), whichconsists of three bones in the middle ear. The third bone of theossicular chain (140), the stirrup (145), contacts the outer surface ofthe cochlea (150) and causes movement of the fluid within the cochlea.Cochlear hair cells respond to the fluid-borne vibration in the cochlea(150) and trigger neural electrical signals that are conducted from thecochlea to the auditory cortex by the auditory nerve (160).

As indicated above, the cochlear implant (300) is a surgically implantedelectronic device that provides a sense of sound to a person who isprofoundly deaf or severely hard of hearing. In many cases, deafness iscaused by the absence or destruction of the hair cells in the cochlea,i.e., sensorineural hearing loss. In the absence of properly functioninghair cells, there is no way auditory nerve impulses can be directlygenerated from ambient sound. Thus, conventional hearing aids, whichamplify external sound waves, provide no benefit to persons sufferingfrom complete sensorineural hearing loss.

As discussed above, the cochlear implant (300) does not amplify sound,but works by directly stimulating the auditory nerve (160) withelectrical impulses representing the ambient acoustic sound. Cochlearprosthesis typically involves the implantation of electrodes into thecochlea. The cochlear implant operates by direct electrical stimulationof the auditory nerve cells, bypassing the defective cochlear hair cellsthat normally transduce acoustic energy into electrical energy.

External components (200) of the cochlear implant system can include aBehind-The-Ear (BTE) unit (175), which contains the sound processor andhas a microphone (170), a cable (177), and a transmitter (180). Themicrophone (170) picks up sound from the environment and converts itinto electrical impulses. The sound processor within the BTE unit (175)selectively filters and manipulates the electrical impulses and sendsthe processed electrical signals through the cable (177) to thetransmitter (180). The transmitter (180) receives the processedelectrical signals from the processor and transmits them to theimplanted antenna (187) by electromagnetic transmission. In somecochlear implant systems, the transmitter (180) is held in place bymagnetic interaction with a magnet in the center of the underlyingantenna (187).

The components of the cochlear implant (300) include an internalprocessor (185), an antenna (187), and a cochlear lead (190) whichterminates in an electrode array (195). The internal processor (185) andantenna (187) are secured beneath the user's skin, typically above andbehind the pinna (110). The antenna (187) receives signals and powerfrom the transmitter (180). The internal processor (185) receives thesesignals and performs one or more operations on the signals to generatemodified signals. These modified signals are then sent along a number ofdelicate wires which pass through the cochlear lead (190). These wiresare individually connected to the electrodes in the electrode array(195). The electrode array (195) is implanted within the cochlea (150)and provides electrical stimulation to the auditory nerve (160).

The cochlear implant (300) stimulates different portions of the cochlea(150) according to the frequencies detected by the microphone (170),just as a normal functioning ear would experience stimulation atdifferent portions of the cochlea depending on the frequency of soundvibrating the liquid within the cochlea (150). This allows the brain tointerpret the frequency of the sound as if the hair cells of the basilarmembrane were functioning properly.

FIG. 2 is an illustrative diagram showing a more detailed view of theexternal components (200) of one embodiment of a cochlear implantsystem. External components (200) of the cochlear implant system includea BTE unit (175), which comprises a microphone (170), an ear hook (210),a sound processor (220), and a battery (230), which may be rechargeable.The microphone (170) picks up sound from the environment and converts itinto electrical impulses. As discussed above, the sound processor (220)selectively filters and manipulates the electrical impulses and sendsthe processed electrical signals through a cable (177) to thetransmitter (180). A number of controls (240, 245) adjust the operationof the processor (220). These controls may include a volume switch (240)and program selection switch (245). The transmitter (180) receives theprocessed electrical signals from the processor (220) and transmitsthese electrical signals and power from the battery (230) to thecochlear implant by electromagnetic transmission.

FIG. 3 is an illustrative diagram showing one embodiment of a cochlearimplant (300), including an internal processor (185), an antenna (187),and a cochlear lead (190) having an electrode array (195). The cochlearimplant (300) is surgically implanted such that the electrode array(195) is internal to the cochlea, as shown in FIG. 1. The internalprocessor (185) and antenna (187) are secured beneath the user's skin,typically above and behind the pinna (110, FIG. 1), with the cochlearlead (190) connecting the internal processor (185) to the electrodearray (195) within the cochlea. As discussed above, the antenna (187)receives signals from the transmitter (180) and sends the signals to theinternal processor (185). The internal processor (185) modifies thesignals and passes them along the appropriate wires to activate one ormore of the electrodes within the electrode array (195). This providesthe user with sensory input that is a representation of external soundwaves sensed by the microphone (170).

FIG. 4 is a partially cut away perspective view of a cochlea (150) andshows an illustrative electrode array (195) being inserted into thecochlea (150). The primary structure of the cochlea is a hollow,helically coiled, tubular bone, similar to a nautilus shell. The coiledtube is divided through most of its length into three fluid-filledspaces (scalae). The scala vestibuli (410) is partitioned from the scalamedia (430) by Reissner's membrane (415) and lies superior to it. Thescala tympani (420) is partitioned from the scala media (430) by thebasilar membrane (425) and lies inferior to it. A typical human cochleaincludes approximately two and a half helical turns of its variousconstituent channels. The cochlear lead (190) is inserted into one ofthe scalae, typically the scalae tympani (420), to bring the individualelectrodes into close proximity with the tonotopically organized nerves.

The illustrative cochlear lead (190) includes a lead body (445). Thelead body (445) connects the electrode array (195) to the internalprocessor (185, FIG. 3). A number of wires (455) pass through the leadbody (445) to bring electrical signals from the internal processor (185,FIG. 3) to the electrode array (195). According to one illustrativeembodiment, at the junction of the electrode array (195) to the leadbody (445) is a molded silicone rubber feature (450). The feature (450)can serve a variety of functions, including, but not limited to,providing a structure which can be gripped by an insertion tool,providing a visual indicator of how far the cochlear lead (190) has beeninserted, and securing the electrode array (195) within the cochlea.

The wires (455) that conduct electrical signals are connected to theelectrodes (465, 470) within the electrode array (195). For example,electrical signals which correspond to a low frequency sound may becommunicated via a first wire to an electrode near the tip (440) of theelectrode array (195). Electrical signals which correspond to a highfrequency sound may be communicated by a second wire to an electrode(465) near the base of the electrode array (195). According to oneillustrative embodiment, there may be one wire (455) for each electrodewithin the electrode array (195). The internal processor (185, FIG. 3)may then control the electrical field generated by each electrodeindividually. For example, one electrode may be designated as a groundelectrode. The remainder of the electrodes may then generate electricalfields which correspond to various frequencies of sound. Additionally oralternatively, adjacent electrodes may be paired, with one electrodeserving as a ground and the other electrode being actively driven toproduce the desired electrical field.

According to one illustrative embodiment, the wires (455) and portionsof the electrodes (470) are encased in a flexible body (475). Theflexible body (475) may be formed from a variety of biocompatiblematerials, including, but not limited to medical grade silicone rubber.The flexible body (475) secures and protects the wires (455) andelectrodes (465, 470). The flexible body (475) allows the electrodearray (195) to bend and conform to the geometry of the cochlea.

FIG. 5 is a diagram of a material which exhibits high charge transfer tocochlear tissues. This material has been formed into a tethered set ofelectrode pads (516) and attached to an underlying sacrificial substrate(502). As used in the specification and appended claims, the term“forming” or “formed” includes a wide variety of subtractive, additive,or transformative processes, including but not limited to, mechanicalremoval of material, laser cutting, electrical discharge machining(EDM), photolithographic techniques and etching, electron beammachining, abrasive flow machining, casting, extruding, stamping,imprinting, molding, and other suitable processes. According to oneillustrative embodiment, a number of generally rectangular electrodepads (512) have been formed along the center of the patterned highcharge transfer material. The electrode pads (512) may have a number ofother shapes including, but not limited to circular, oval, square, ortrapezoidal. Further, the shape and size of the electrode pads may varythroughout the tethered set (516). In some embodiments, it may bedesirable to form the sheet into shapes with at least some threedimensional curvature.

Each electrode pad (512) is tethered to rails (504) by two tethers(506). As used in the specification and appended claims, the term“tether” or “tethered” refers to a connection between an electrode andthe structure that holds the electrodes in a fixed spatial relationshipwith other electrodes. Ordinarily, the tether (506) has a relativelysmall cross-section compared to the electrode pad (512) and connects theperimeter of the electrode pad (512) and the rails (504). The tethers(506) can hold the electrode pads (512) rigidly in place to completelyfix the electrode spacing or semi-rigidly such that they are close totheir final spacing and can be put into an alignment fixture to adjustthe final spacing. In one embodiment, tether widths are between 50 and250 microns and lengths of the tethers are between 100 and 500 microns.According to one illustrative embodiment, the electrode pads (512) andtethers (506) are formed from a single sheet of high charge transfermaterial.

According to one illustrative embodiment, the high charge transfermaterial may be iridium or an iridium alloy. For example, iridium couldbe activated by exposing it to a number of electrochemical cycles in awater-based electrolyte to develop an activated iridium oxide surface.This activated iridium oxide surface has a higher area and greatercharge transfer characteristics than the underlying iridium material.The electrochemical activation of the iridium surface could be performedbefore or after the assembly of the electrode array.

The high charge transfer material may be patterned using a number oftechniques including, but not limited to, short pulse lasermicromachining techniques. As used in the specification and appendedclaims, the term “short pulse” means pulses less than a nanosecond, suchas in the femtosecond to hundreds of picosecond range. A variety oflasers can be used. For example, very short pulse laser machining may beperformed using a picosecond laser, at UV, visible, or IR wavelengths.These very short pulse lasers can provide superior micromachiningcompared with longer pulse lasers. The very short pulse lasers ablateportions of the material without significant transfer of heat tosurrounding areas. This allows the very short pulse lasers to machinefine details and leaves the unablated material in essentially itsoriginal state.

The set (516) of tethered electrode pads (512) is fixed to a sacrificialsubstrate (502). According to one illustrative embodiment, thesacrificial substrate (502) may be an iron strip which is approximatelythe width of the electrode pads (512) and at least as long as thetethered set (516) of electrode pads. The tethered set (516) ofelectrode pads may be attached to the sacrificial substrate (502) in avariety of ways, including resistance welding or laser welding. One ormore weld joints (508) can be made for each electrode pad (512). Thespacing of the electrode pads (512) is initially maintained by thetethers (506). The tethers (506) are cut after the welds (508) areformed. According to one illustrative embodiment, the tethers (506) arecut at or near the dotted lines (514). After the tethers (506) are cut,the iron strip (502) maintains the desired electrode pad (512) spacingand orientation.

FIG. 6 is a diagram of an illustrative tethered set (500) of winged tabs(513) which have been machined from a flexible electrically conductivematerial. As used in the specification and appended claims, the term“flexible material” or “flexible electrically conductive material”refers to a material with a thickness of 20 to 1000 microns which can becreased or folded at greater than 90 degree angles without significantcracking or other failure at the crease or fold. For example, someplatinum and platinum alloys are flexible materials according to thisdefinition. According to one illustrative embodiment, the tethered set(500) of winged tabs includes a series of winged tabs (513) which aremachined from a platinum or platinum alloy foil using short pulse lasermachining. For example, the sheet material may be between 20 and 50micron thick platinum or platinum alloy (such as platinum/iridium havingup to 20% iridium).

As discussed above, after the tethers (506, FIG. 5) have been cut fromthe electrode pads (512, FIG. 5), the electrode pads remain fastened tothe sacrificial substrate (502). The tethered set (500) of winged tabsis aligned over the electrode pads so that a base portion (520) overlieseach electrode pad (512, FIG. 5). The position of the underlyingelectrode pads is illustrated by the dashed line (522). A variety ofmethods could be used to connect the tethered set (500) of winged tabsto the electrode pads (512), including resistance or laser spot welding.

The dashed trapezoid illustrates the wing portions (525), which will befolded up to contain the wires. The wings (525) may have severaladditional features, such as holes (515). According to one illustrativeembodiment, during a later manufacturing step, a fluid matrix such asliquid silicone rubber is injected into a mold which contains theelectrodes and their associated wiring. The fluid matrix flows throughthe holes (515), and then cures to form the flexible body. The holes(515) provide a closed geometry through which the fluid matrix can gripthe electrode assembly.

A second dashed rectangle outlines a flap (530), which will be foldedover a wire and welded to mechanically secure it to the electrode. Thiswire provides electrical energy to the electrode. The spacing (535) ofthe winged tabs (513) along the rails (505) matches the pitch of theunderlying electrode pads (512, FIG. 5). The pitch of the electrode pads(512, FIG. 5) and the winged tabs (513) is also the pitch of thecompleted electrode assemblies in the final electrode array.

One or more welds (524) are made to join each of the winged tabs (513)to the underlying electrode pads (512, FIG. 5). A thin coating ofsilicone or other biocompatible insulating material can be depositedover an inner surface of the electrodes and wings and cured. Thissilicone layer provides a compliant and electrically insulating layerbetween the wires and the electrodes. The silicone layer can preventmechanical abrasion and/or electrical shorting of the wires. Accordingto one illustrative embodiment, the wires are also individuallyinsulated. For example, the wires may be individually insulated by aparylene coating. The tethers (510) are then cut and the tethers andrails (505) are removed.

FIG. 7A is a perspective diagram of an illustrative composite electrodeassembly (750) which forms an integral wire carrier. The overall size ofthe finished electrode assembly (750) may be on the order of millimetersor less than a millimeter, with feature sizes on the order of tens tohundreds of microns. To form the electrode assembly, the flap (730) ofthe winged tab is folded over a selected wire and welded to electricallyand mechanically secure the wire to the winged tab. The wings (725) arebent in two locations, once near the base (720) and again at the notches(745) to form a rectangular wire carrier around the wires (765). In itsfolded form, the winged tab forms a support structure which is both awire carrier and a support to the underlying electrode pad (512).

FIG. 7B is a cross sectional diagram of the composite electrode assembly(750) shown in FIG. 7A. As discussed previously, the electrode pad (512)is on the underside of the electrode assembly (750). The electrode pad(512) may have a thickness which is equal to, less than, or greater thanthe thickness of the flexible conductive material which makes up thewinged tab. In general, the electrode pad (512) may have any thicknesssuitable to a desired application.

According to one illustrative embodiment, all of the electrodeassemblies for a single cochlear implant are machined from the twosheets of conductive material, one flexible sheet of material and theother high charge transfer sheet of material. For example, the electrodepads and winged tabs can be machined from a flexible sheet of conductivematerial at their desired spacing in the cochlear lead and be held inplace to an outer frame by small tethers. The winged tabs can be formedwith a number of features that facilitate the final assembly of thecochlear lead. As discussed above, precision short pulse laser machiningand automated alignment of the components can reduce the amount ofmanual work required and improve yields.

FIG. 8A is a perspective view of another illustrative embodiment of acomposite electrode assembly (800), which includes an integral wirecarrier and an electrode pad (512) welded on the bottom of the foldedwinged tab. For clarity of illustration, the wires are not shown in FIG.8A. As discussed above, the flap (530) is folded over the wireassociated with this composite electrode assembly (800) and welded toelectrically and mechanically secure it in place. The wings (525) arefolded up to secure the wires for the more distal electrodes and form abundle of wires which passes back along the electrode array to thecochlear lead and to the internal processor. The electrode pad (512) ison the underside (520) of the folded winged tab (530). The electrode pad(512) is not covered by the flexible body and is consequently exposed tothe body tissues and fluids within the cochlea. The activated surface ofthe electrode pad (512) transfers electrical charge from the connectedwire to the tissues. As discussed above, the electrode pad (512) may beformed from a variety of materials. According to one illustrativeembodiment, the electrode pad (512) has an activated iridium oxide layeron its external surface. The activated iridium oxide layer may have acharge transfer capability of approximately 3 to 7 mC/cm̂2. This chargetransfer is significantly greater than a smooth platinum surface whichtypically has a charge transfer capability of approximately than 1mC/cm̂2. The transferred charge creates an electrical field through thesurrounding tissues, thereby stimulating the adjacent auditory nerve.

FIG. 8B is a cross-sectional view of the composite electrode assembly(800) shown in FIG. 8A. Cross-sections of the wires (810) are shown in awire bundle (805) contained by the wings (525). As discussed above, thiswire bundle (805) passes through the entire length of the electrodearray (195, FIG. 3); however, each individual wire within the bundleterminates at the electrode to which it is welded.

FIG. 9 shows a cross-sectional view of a cochlear electrode (900). Acomposite electrode assembly (902) is partially embedded in the flexiblebody (915). The composite electrode assembly (902) includes a supportstructure (904) and an electrode pad (512) which is attached to thebottom surface (905) of the support structure (904). According to oneillustrative embodiment, the partial encapsulation of the compositeelectrode assembly (902) is performed using a mold and a liquidinjection molding process. The composite electrode assembly (900) ispositioned in the mold and the mold is closed. A curable liquid, such asa medical grade liquid silicone rubber, is then injected into the mold.After encapsulation, the curable liquid is then cured and the assemblyis removed from the mold.

The curable liquid fills voids within the composite electrode assembly(902) and entirely encapsulates it except for one surface of theelectrode pad (512). This allows the electrode pad (512) of eachcomposite electrode assembly (902) to contact the tissue in the cochleawhere each electrode is located after inserting the lead into thecochlea. The high charge transfer at the surface of the electrode pad(512) provides for more efficient stimulation of the cochlear tissuethan if the conductive material of the winged tab were used as thestimulating surface.

FIG. 10 shows a flowchart (1000) of a method forming a cochlearelectrode array. The method includes forming a first foil into atethered set of electrode pads (step 1005). The tethered set ofelectrode pads is mechanically attached to a sacrificial substrate andthe tethers are cut (step 1010). A second foil of flexible electricallyconductive material is formed into a tethered set of winged tabs (step1015). The tethered set of winged tabs is then attached to the electrodepads and the tethers cut to release the winged tabs (step 1025). Theappropriate wires can then be connected to the corresponding electrodeassemblies. According to one illustrative embodiment, the wire isattached to the winged tabs by folding a tab over the wire and weldingthe tab in place to hold the wire (step 1030). The remaining wires areshaped into the desired wire bundle geometry by folding up the wings(step 1035). The sacrificial substrate can then be removed and theelectrode array encapsulated in a flexible polymer body (step 1040). Inembodiments where the sacrificial substrate is an iron strip, the ironstrip can be removed using a selective acid etch. The oxidization etchis tailored such that the iron strip is removed, but the materials ofthe electrode assembly are not affected.

FIGS. 11, 12 and 13 describe an alternative method for creating acochlear electrode array. FIG. 11 is a diagram showing a tethered set(501) of winged tabs being attached to a sacrificial strip (502). Inthis embodiment, the tethered set (501) of winged tabs (513) is similarto that which was previously described in FIG. 6. One significantdifference is that a central portion of the winged tabs (513) has beenremoved to form a window or central aperture (523) in each winged tab(513). The central aperture (523) is formed in the base portion of thewinged tabs (513). According to one illustrative embodiment, the size ofthe central aperture (523) is maximized while retaining sufficientmechanical strength in the winged tabs (513) to support the wings (525)and tab (530). As discussed above, the tethered set (501) of winged tabscan be attached to the sacrificial strip (502) using a variety ofmethods including weld joints (524). The tethers (510) can then be cutor broken to free the winged tabs (513), which are then held in place bythe sacrificial strip (502) and weld joints (524).

FIG. 12 is a diagram which shows an illustrative tethered set (511) ofelectrode pads being joined to the winged tabs (513). As discussedabove, the set of electrodes could be formed from a material which has arelatively high charge transfer from the electrode pads (512) into thesurrounding tissues and fluids of the cochlea. According to oneillustrative embodiment, the electrode pads (512) could be formed fromiridium which has a layer of activated iridium oxide. As discussedabove, the electrode pad (512) has an activated iridium oxide layer onits external surface. The charge transfer of the activated iridium oxidelayer is significantly greater than a smooth platinum. Charge transfersfrom the iridium oxide layer as high as 40 mC/cm̂2 are possible, butcharge transfers at this level could irreversibly damage the iridiumoxide layer. Without being bound to any particular theory, it appearsthat iridium oxide films inject charge via reversible reduction andoxidization between Ir³⁺/Ir⁴⁺ valance states.

The tethered set (511) of electrode pads is aligned with the winged tabs(513) and then fastened in place. As discussed above, one method offastening the winged tabs (513) and the electrodes together isresistance or laser spot welding. The tethers (506) can then be cut orbroken along the dashed line (514).

Although a sacrificial strip (502) is illustrated as a means for holdingthe winged tabs (513) and electrode pads (512) in place, a wide varietyof other techniques could be used. For example, the winged tabs (513)and/or electrode pads (512) could be placed on an adhesive surface. Theadhesive surface would hold the various components in place through theassembly process. The adhesive surface could then be removedmechanically or chemically. For example, a solvent such as acetone orisopropyl alcohol could be used to facilitate the removal of theadhesive surface. Additionally or alternatively, a wax or othercompliant surface could be used to hold the various components in place.For example, the winged tabs could be pressed into a wax surface orother deformable surface. After the assembly process, the wax could beremoved by heating.

FIG. 13 shows a cross sectional diagram of the illustrative electrodeassembly illustrated in FIGS. 11 and 12 after the assembly andencapsulation processes are complete. As was previously discussed, theelectrode pad (512) may be joined to a winged tab (513) by weld joints(524). The electrode pad (512) covers the central aperture (523) in thewinged tab (513). One of the tabs (530) is folded over a designated wire(1305). This brings the wire (1305) into direct contact with theelectrode pad (512). The wire (1305) may be secured in a number of waysincluding forming additional weld joints (1315) between the folded tab(530) and the electrode pad (512). Additionally or alternatively, weldjoints (1320) can be made which directly electrically attach the wire(1305) to the electrode pad (512) and/or the overlying tab (530).

After the designated wire (1305) is secured in place, the wings can befolded up to form a wire bundle (1310) which contains the wires whichcontinue through the cochlear electrode array to provide current toother electrodes. The sacrificial substrate can then be removed and theentire electrode array can be partially encased in a silicone rubberbody (1300), leaving the outer surface of electrode pad (512) exposedthrough the central aperture (523).

This alternative method may have a number of advantages. For example,the electrode surface is somewhat recessed, which may protect it fromdamage. Additionally, because the electrode pads are not welded to thesacrificial strip and are not bent during the assembly process, morefragile surface layers can be used on the electrode pads to improve thecharge transfer of the electrode.

FIG. 14 is a cross sectional diagram of a cochlear electrode (1400),which includes an electrode substrate (1405) that has a surface layer(1410) which increases its charge transfer capability. Together, theelectrode substrate (1405) and surface layer (1410) form the electrodepad (1404). According to one illustrative embodiment, the surface layer(1410) can increase the charge transfer capability of the cochlearelectrode (1400) primarily by increasing the surface area compared tosmooth platinum. This can be done by “activating” a surface of theelectrode pad (1404) or by depositing a coating on the surface of theelectrode pad (1404). Examples of depositing a coating on the surface ofthe electrode pad (1404) may include depositing a thin film such assputtered iridium oxide, titanium nitride, ruthenium oxide, porousniobium oxide, or activated carbon. Other examples of structures whichincrease the surface area of the electrode pad (1404) include depositingor forming platinum grey, platinum black, sintered platinum,nanostructures, or other appropriate structures which have high surfaceareas on the electrode substrate (1405). As described in U.S. Pat. Nos.6,974,533 and 5,751,011, platinum gray refers to a platinummicrostructure which has a significantly larger surface area than smoothplatinum and forms a relatively strong and adhesive film.

Platinum black is a fine powder of platinum which can be deposited overa solid platinum substrate. This process produces a surface area whichis much higher than the geometric surface area of the underlyingsubstrate and exhibits charge transfer characteristics which aresuperior to non-textured platinum surfaces. The platinum particles aretypically sprayed or hot pressed onto the substrate layer. According toone illustrative embodiment, platinum black may be electroplated onto aplatinum substrate. The platinum substrate is first cleaned, and thenplaced in a water solution which contains chloroplantanic acid and leadacetate. An electrical current is then passed through the water solutionsuch that chlorine evolves at the anode and deposits platinum blackparticles on the platinum substrate.

While iridium oxide films are known to have charge transfercharacteristics which are superior to most forms of platinum, theiridium oxide films are also known to be brittle and have delaminatingproblems when the underlying surface is bent. To avoid this, the filmsand structures described above could be deposited on the electrodesubstrate (1405) which is not required to flex during the manufacture oruse of the electrode array.

Many of these films and structures could be damaged if they weredirectly deposited or produced on a winged tab which is then folded intothe electrode/wire carrier configuration. For example, structuredplatinum, such as platinum black, platinum gray, sintered platinum,platinum nanoparticles, and platinum metal sponges can all be sensitiveto folding or welding of the underlying substrate, tending to crack ordelaminate from the substrate.

According to one illustrative embodiment, the electrode pad (512) may bea layer that is deposited directly on the bottom of the winged tabrather than on a separate piece of material. For example, the electrodepad (512) may be formed by depositing iridium on the base of a platinumwinged tab. This deposition could be carried out by electroplating,electroless plating, sputter coating, vapor phase deposition, pulsedlaser deposition, or other suitable methods. According to oneillustrative embodiment, an iridium oxide film is sputtered onto thesurface using DC reactive sputtering from an iridium metal target in anoxidizing environment. The thickness of the sputtered film may be fromabout 100 nanometers to several microns. This can result in acharge-injection capacity which is between 1 and 9 mC/cm̂2, which iscomparable to an activated iridium oxide electrode pad. Additionally oralternatively, an iridium film may be deposited onto the surface andsubsequently activated as described above.

According to one illustrative embodiment, iridium oxide nanoparticlescould be joined to form a high surface area layer (1410) over theelectrode substrate (1405). A wide variety of iridium oxidenanoparticles could be used, including nanoparticles which arespherical, faceted, nanorods, nanowhiskers, nanopyramids, and othershapes. Iridium oxide nanoshapes with a size between 20 and 80nanometers can have a surface area of 10 to 50 square meters per gram.Larger nanoshapes which have a size of 100 nanometers can have surfaceareas of approximately 7 to 10 square meters per gram. These highsurface areas, combined with the intrinsically high charge transfercharacteristics of the iridium oxide can produce an electrode with avery high rate of charge transfer. These iridium oxide nanoparticlescould be joined by sintering, embedding in a matrix, or by other means.In other embodiments, the iridium oxide nanoparticles could be growndirectly on an iridium oxide substrate.

A variety of techniques and materials can be used to improve themechanical and electrical properties of the thin films and structures.According to one illustrative embodiment, an iridium oxide thin film isdeposited over a roughened platinum surface. For example, a platinumgray layer may be deposited over the platinum substrate (1405). Thisproduces a microporous structure over the platinum which has goodadhesion to the underlying platinum substrate. An iridium oxide thinfilm layer may then be deposited over the high surface area platinumgray layer. Because the iridium oxide thin film is deposited on atextured surface, its surface area and its adhesion to the surface isincreased.

Additionally or alternatively, the adhesion of a sputtered iridium oxidelayer may be improved by initially sputtering a combination of platinumand iridium oxide onto a platinum substrate (1405), and then graduallychanging the composition to include more iridium oxide until onlyiridium oxide is deposited. This graduated coating may improve theadhesion and charge transfer between the platinum substrate (1405) andthe iridium layer (1410).

As described above in FIGS. 11-13, the electrode pad (1405) may bejoined to a winged tab (513, FIG. 12) by weld joints (1425). Althoughforming the weld joints (1425) may damage the thin film or structure ofthe surface layer (1410) in the weld joint region, this will not impairthe structure or overall charge transfer of the portion of the surfacelayer (1410) that is exposed to the cochlea through the window (523).The assembly process then proceeds as previously described. A tab (530)is folded over a designated wire and the tab (530) and the wire arewelded in place. The resistance or laser welding process is adjusted sothat the welds (1415) join the tab (530) and wire to the electrode pad(1405) without disrupting the surface layer (1410).

FIG. 15 is a flowchart which shows one illustrative method for forming acochlear electrode array. According to one illustrative embodiment, aflexible electrically conductive material is formed into a tethered setof winged tabs which have a window within each winged tab (step 1505).As discussed above, the flexible electrically conductive material may beplatinum or a platinum alloy. The tethered set of winged tabs is fixedto a sacrificial substrate and the tethers are cut (step 1510). A highcharge transfer material is formed into a set of tethered electrodepads. For example, the high charge transfer material may be an iridiumbased material and the forming process may be short pulse lasermachining.

The tethered set of electrode pads is attached to the set of winged tabssuch that an electrode pad covers the central aperture in each wingedtab and the tethers are cut from the electrode pads (step 1520). Thewires are attached to the winged tabs by folding a tab over a selectedwire and welding the wire in place. The remaining wires are formed intoa bundle by folding up the wings (step 1525). This process is repeatedfor each electrode assembly in the array until all of the wires areconnected to an electrode pad and properly formed into the wire bundle.The sacrificial substrate can then be removed and the electrode arrayencapsulated (step 1530).

The process described above is only one illustrative method for forminga cochlear electrode array. The steps may be performed in a variety oforders and a number of additional steps may be used. For example, step1515 can occur any time before step 1520. Additional steps, such assurface preparation, testing, or other steps, can be included in theprocess.

The preceding description has been presented only to illustrate anddescribe embodiments and examples of the principles described. Thisdescription is not intended to be exhaustive or to limit theseprinciples to any precise form disclosed. Many modifications andvariations are possible in light of the above teaching.

1. A method of forming a charge transferring surface, the methodcomprising: partially encapsulating an electrode in a flexible body; andsubsequently electrochemically activating a first exposed portion of theelectrode to form an iridium oxide surface, the iridium oxide surfacehaving a greater charge transfer density than an unactivated exposedportion of the electrode.
 2. The method of claim 1 wherein the firstexposed portion of the electrode is in a recess and the iridium oxidesurface does not extend beyond the recess.
 3. The method of claim 1,further comprising a second exposed portion of the electrode inelectrical contact with the first exposed portion of the electrode,wherein the second exposed portion of the electrode does not form aniridium oxide surface when exposed to the same electrochemicalactivation as the first exposed portion.
 4. The method of claim 3,wherein the first exposed portion of the electrode is part of anelectrode pad comprising iridium and the second exposed portion of theelectrode is part of a winged tab.
 5. The method of claim 3, wherein thesecond exposed portion of the electrode is composed of platinum.
 6. Themethod of claim 3, wherein the first exposed portion is a bottom surfaceof a recess, the second exposed portion is a side of the recess, and theiridium oxide surface does not extend beyond the recess.
 7. The methodof claim 3, wherein a connection between the first exposed portion andthe second exposed portion of the electrode is free of activated iridiumoxide.
 8. A method for controlling element separation in a physicalarray, the method comprising: fixing multiple tethered electrode arrayelements to a temporary substrate with predetermined separations betweenthe multiple tethered electrode array elements; removing tethers of themultiple tethered electrode array elements to form multiple untetheredelectrode array elements; forming a flexible body that connects themultiple untethered electrode array elements at the predeterminedseparations; and separating the temporary substrate from the multipleuntethered electrode array elements.
 9. The method of claim 8, whereinseparating the temporary substrate from the multiple untetheredelectrode array elements comprises dissolving a portion the temporarysubstrate.
 10. A method for forming an electrode in a cochlear electrodearray, comprising: forming a first foil of electrically conductivematerial into a set of winged tabs; forming a second foil into a set ofelectrode pads; fixing a sacrificial substrate to one of: a winged taband an electrode pad; attaching the set of winged tabs and the set ofelectrode pads together; and electrically connecting a selected wire toeach of the winged tabs.
 11. The method of claim 10, further comprising:bending a wing of each winged tab to constrain additional wires passingover the winged tab to form a wire bundle; removing the sacrificialsubstrate to form an electrode assembly; and partially encapsulating theelectrode assembly in a flexible polymer body.
 12. The method of claim10, in which forming the first and second foil comprises short pulselaser machining
 13. The method of claim 10, in which forming the firstfoil comprises forming a tethered set of winged tabs and forming asecond foil comprises forming a tethered set of electrode pads.
 14. Themethod of claim 13, further comprising cutting tethers of the tetheredset of winged tabs after attaching the winged tabs and the electrodepads together.
 15. The method of claim 10, in which the sacrificialsubstrate comprises an iron strip.
 16. The method of claim 10, furthercomprising electrochemically activating an iridium material bysubjecting a surface of the iridium material to a number ofelectrochemical cycles in a water-based electrolyte such that thesurface of the iridium material develops an activated iridium oxidelayer which has electrical charge transfer which is superior to theelectrically conductive material which makes up the set of winged tabs.17. The method of claim 10, in which the electrode pad is first attachedto the sacrificial substrate and then attaching the winged tab and theelectrode pad together.
 18. The method of claim 10, further comprising:forming an aperture in the winged tab; attaching the winged tab to thesacrificial substrate; and attaching the electrode pad over the aperturein the winged tab.
 19. The method of claim 10, in which the electrodepad and winged tab are attached using a resistance weld.
 20. The methodof claim 10, in which the electrode pads comprise a surface modified tobe exposed to cochlear tissue and fluid, the surface having a chargetransfer to the cochlear tissue and fluid that is higher than that of anunmodified substrate material.